It is known that acrylamide is formed in several food materials during heating to high temperatures. The acrylamide formation has been ascribed to a Maillard reaction wherein asparagine is one of the reactants. It is well known that acrylamide formation in heated food products may be reduced by a treatment reducing the amount of asparagine in the food materials, such as by subjecting the food materials to the action of the enzyme asparaginase (see e.g. WO2004/026042 (Frito-Lay North America, Inc.)).
A number of microbial asparaginases have been identified; see e.g. WO2004/030468 (DSM) disclosing the sequence of an asparaginase derived from Aspergillus niger, or WO2004/032648 (Novozymes A/S) disclosing sequences of asparaginases derived from Aspergillus oryzae and Penicillium citrinum. WO2004/032648 also mentions the amino acid sequences of asparaginases from Aspergillus fumigatus and Aspergillus nidulans. The amino acid sequence of an asparaginase from Aspergillus terreus can be obtained from the UniProt database (accession no. q0cwj1).
The amino acid sequence and the crystal structure of an L-asparaginase from Erwinia chrysanthemi have been described (Jacek Lubkowski, Miroslawa Dauter, Khosrow Aghaiypour, Alexander Wlodawera and Zbigniew Dauter (2003) Atomic resolution structure of Erwinia chrysanthemi L-asparaginase. Acta Cryst. D, 59, 84-92).
A method for designing proteins with improved thermal stability using 3-isopropylmalate dehydrogenase from Thermus thermophilus as a model enzyme has been described (Watanabe, K. et al. (2006) J. Mol. Biol. 355, 664-674).
For some applications, asparaginases having improved properties are desired, such as asparaginases having improved thermotolerance, e.g. improved thermostability or improved activity at high temperatures.
It is an object of the present invention to provide alternative asparaginases, in particular novel asparaginases having improved properties. Such improved asparaginases are suitable for use, e.g. in the production of food products.